The invention relates to a duct element for the exhaust system of a motor vehicle with an internal combustion engine, which duct element comprises at least one flexible duct part, preferably a metallic annular corrugated hose or bellows. Within the scope of this description the term “exhaust system” includes not only exhaust ducts but explicitly also exhaust return lines, unless specified otherwise.
Additionally the invention relates to a decoupling element for motor vehicles with an internal combustion engine, preferably for exhaust ducts or exhaust return lines as well as the use of certain materials.
Commonly stainless austenitic steel, preferably so-called standard austenite is used, e.g., the materials 1.4301, 1.4541, or 1.4571 (which are commonly known stainless steel types having specified weight percentages (wt %) for their components, including Fe, C, Mn, Si, P, S, Cr, Ni, and N) for decoupling elements used in exhaust systems of motor vehicles with internal combustion engines in order to decouple oscillations induced by the internal combustion engine from other components of the exhaust system. On the one hand, duct elements used in this area must tolerate high thermal stress due to the temperature of the exhaust flow passing through them, and on the other hand, they must be particularly resistant to corrosion at least at their exterior, because during use in and/or on motor vehicles such duct elements are exposed to moisture and other corrosive media, particularly brine.
To the extent that constituent components of steel are referred to herein in connection any specified steel grades, they are weight percentages in accordance with standard practice in the steel industry.
Accordingly it is known in prior art to use nickel based materials, e.g., 2.4856, for the exhaust system of a motor vehicle at least for the exterior sections of duct elements. In this way, a particularly high corrosion resistance is yielded, however it is disadvantageous here that nickel-based materials are much more expensive than the standard austenite mentioned at the outset.
Due to the fact that the corrosion resistance of standard austenite, for example 1.4571, is insufficient for certain purposes of use an interim solution seems desirable in many applications, in which both the price as well as the corrosion resistance of the material ranges between the respective values for the materials 1.4571 and 2.4856. In order to attain this objective, in the past steel manufacturers have become active and developed specific alloys and applied for patent protection. This relates to the materials Incoloy 864 and Incoloy 865 of Special Metals as well as the materials 332Mo and 334Mo of Allegheny.
In this context it has been shown to be disadvantageous, however, that the price-benefit ratio of the above-mentioned steel developments Incoloy 864/865, 332Mo, and 334Mo is relatively unfavorable. Additionally, repeated price increases or supply problems have occurred in the past due to the strictly limited supply situation.